Finely divided polymers gelled by crosslinking reactions in the particles and processes for producing same have been so far widely known. For example, there are a process in which a monomer mixture containing a monomer for crosslinking containing at least two ethylenic double bonds is emulsion polymerized in an aqueous medium (British Patent No. 967,051 and European Patent Application Publication No. 259181A), and a process in which a monomer mixture containing glycidyl (meth)acrylate and (meth)acrylic acid is dispersion polymerized in the presence of a dispersion stabilizer in a non-aqueous medium, and simultaneously these functional groups are reacted (U.S. Pat. No. 4,025,474). Especially, as a process for producing a polymer in an aqueous medium using an alkoxysilane monomer, there are proposed a process in which a mixture of an alkoxy silane monomer and the other monomer is emulsion polymerized in an aqueous medium using a non-reactive surface active agent (European Patent Application Publication No. 153,600A), a process for obtaining a delustered electrodeposition-coated film for aluminum building material in which an alkoxysilane monomer, (meth)acrylic acid and the other monomer are copolymerized and the resulting copolymer is then dispersed in water (Japanese Laid-Open Patent Application No. 67,396/1984), a water-soluble composition obtained by combining an acrylic polymer containing an alkoxy silane group and a carboxyl group with a colloidal silica (Japanese Patent Publication No. 47,178/1986), and a process in which an acrylic copolymer containing an alkoxysilane group and a cationic group is dispersed in water and the dispersed copolymer is subjected to cross-linking in particles (European Patent Application Publication No. 282000A).
The finely divided gelled polymers obtained by the conventional processes are added to a paint composition and influence rheological characteristics and physical characteristics of the paint composition, contributing to improvements in spray efficiency of the paint, prevention of sagging of the coated film and pattern control of a metallic pigment.
Meanwhile, cationically electrodepositable paints that find wide acceptance mainly in automobile industry have per se an excellent corrosion resistance, but the coated film in the edge portion of the coated product does not become thick and is poor in edge covering property; its improvement has been demanded. In order to solve the above problem, the present inventors have made investigations to apply the aforesaid finely divided gelled polymer to the cationically electro-depositable paint. Nevertheless, most of the known finely divided gelled polymers are non-aqueous dispersions or aqueous dispersions of an anionic or nonionic type obtained by emulsion polymerization using a non-reactive surface active agent, and it is usually difficult to apply them to a cationically electrodepositable paint. Even if they are applied to the cationically electro-depositable paint, the stability of electrodeposition coating bath and electrodepositable characteristics as well as the water resistance and corrosion resistance of the coated film are impaired. Accordingly, they cannot endure the practical use in this field.
On the other hand, the present inventors have proposed an internally crosslinked, finely divided gelled polymer having an alkoxysilane group, a hydroxyl group and a cationic group, and a process for producing same (UK Patent Application No. 2,221,689A and DT-OS 3926326). Said internally crosslinked, finely divided gelled polymer has cationically electrodepositable characteristics. Even if said polymer is added to a cationically electrodepositable paint, the stability of bath and electrodepositable characteristics are not impaired. The baked, coated film is excellent in edge covering property but still a bit inferior in corrosion resistance in wet condition and thus unsatisfactory in the practical use.